fs: Buffer and encoding enhancements to fs API

This makes several changes:

1. Allow path/filename to be passed in as a Buffer on fs methods
2. Add `options.encoding` to fs.readdir, fs.readdirSync, fs.readlink,
   fs.readlinkSync and fs.watch.
3. Documentation updates

For 1... it's now possible to do:

```js
fs.open(Buffer('/fs/foo/bar'), 'w+', (err, fd) => { });
```

For 2...
```js
fs.readdir('/fs/foo/bar', {encoding:'hex'}, (err,list) => { });

fs.readdir('/fs/foo/bar', {encoding:'buffer'}, (err, list) => { });
```

encoding can also be passed as a string

```js
fs.readdir('/fs/foo/bar', 'hex', (err,list) => { });
```

The default encoding is set to UTF8 so this addresses the
discrepency that existed previously between fs.readdir and
fs.watch handling filenames differently.

Fixes: https://github.com/nodejs/node/issues/2088
Refs: https://github.com/nodejs/node/issues/3519
PR-URL: https://github.com/nodejs/node/pull/5616
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>

1 files changed, 31 insertions, 0 deletions

diff --git a/test/parallel/test-fs-readdir-ucs2.js b/test/parallel/test-fs-readdir-ucs2.js
new file mode 100644
index 0000000000..578723117a
--- /dev/null
+++ b/test/parallel/test-fs-readdir-ucs2.js
@@ -0,0 +1,31 @@
+'use strict';
+
+const common = require('../common');
+const path = require('path');
+const fs = require('fs');
+const assert = require('assert');
+
+if (process.platform !== 'linux') {
+  console.log('1..0 # Skipped: Test is linux specific.');
+  return;
+}
+
+common.refreshTmpDir();
+const filename = '\uD83D\uDC04';
+const root = Buffer.from(`${common.tmpDir}${path.sep}`);
+const filebuff = Buffer.from(filename, 'ucs2');
+const fullpath = Buffer.concat([root, filebuff]);
+
+fs.closeSync(fs.openSync(fullpath, 'w+'));
+
+fs.readdir(common.tmpDir, 'ucs2', (err, list) => {
+  if (err) throw err;
+  assert.equal(1, list.length);
+  const fn = list[0];
+  assert.deepStrictEqual(filebuff, Buffer.from(fn, 'ucs2'));
+  assert.strictEqual(fn, filename);
+});
+
+process.on('exit', () => {
+  fs.unlinkSync(fullpath);
+});